Radio frequency power amplifiers (RF PAs) are essential for use in mobile devices, such as, but not limited to, smartphones, mobile computing devices (e.g., tablet computers), and other applications. The modern trend is for RF PAs with higher efficiencies, smaller form factors, and lower manufacturing costs.
An RF PA based on standard CMOS technologies often exhibits poor performance, due at least in part to low efficiency, low breakdown voltage and poor linearity, among other factors, thus limiting its application. Known techniques for improving the performance of CMOS-based RF PAs have been largely unsuccessful. For example, in attempting to increase the voltage capability of a CMOS-based RF PA, cascading techniques have been employed, which generally involves stacking multiple N-channel metal-oxide-semiconductor (NMOS) devices together to thereby distribute the supply voltage across the multiple devices. However, controlling the multiple gates of these stacked devices simultaneously requires a complex gate bias network, which is often highly sensitive to variations in process, voltage and/or temperature (PVT) conditions to which the device is subjected. Furthermore, the stacked NMOS devices may cause an increase in channel resistance and a decrease in transconductance, which is undesirable. To compensate for the lower transconductance of the cascaded NMOS device arrangement, large-area devices can be used. However, this comes at the expense of increased junction capacitance, which deteriorates the high-frequency capability of the RF PA.